1. Field of the Invention
The present invention relates to a lens barrel having a magnification-varying function and a photographing apparatus including the same. Particularly, the invention relates to an improvement in the strength of the lens barrel or the photographing apparatus.
2. Description of Related Art
For varying the magnification of a lens barrel having a magnification-varying function by moving a plurality of lens groups thereof, there is employed a lens barrel including in combination a plurality of rotation cylinders which rotate along the optical axis and a plurality of straight-moving cylinders which move straight along the axis, wherein the positions of the plurality of lens groups are varied by protruding/retracting the barrel electrically or manually.
For example, in a lens barrel of Japanese patent laid-open No. 2004-54027 as partially shown in a sectional view of FIG. 11, a straight-moving cylinder 52 and a rotation cylinder 53 are prevented from rattling by the following construction. That is, a tip portion of an outer circumference of a straight moving cylinder 52 is provided with taper guiding pins 54 each having a tapered guiding surface and parallel guiding pins 55 each having parallel guide faces in section, and an inner circumferential surface of the rotation cylinder 53 is provided with spiral cam grooves with which the taper guiding pins 54 and the parallel guiding pins 55 are engaged, whereby the straight moving cylinder 52 can be moved forward and backward by way of rotating the rotation cylinder 53.
In the barrel, if external force is applied to the straight-moving cylinder 52 from the optical axis direction, it may be that the applied external force causes the tapered guiding surfaces of the taper guiding pins 54 to move in a radial direction of the lens barrel while sliding along slant side surfaces of the cam grooves, and the taper guiding pins 54 and the parallel guiding pins 55 are disengaged from the cam grooves, rendering the lens barrel inoperative. For preventing such inoperativeness, springs 56 are disposed on sides opposite to the tapered guiding surfaces of the taper guiding pin 54, so that disengagement of the parallel guiding pins 55 from the cam grooves can be avoided by moving only the taper guiding pins 54 in the radial direction of the barrel when external force is applied from the optical axis direction to the straight-moving cylinder 52.
As described above, although springs 56 are disposed on the opposite side to the tapered guiding surfaces of the taper guiding pins 54 so that only the taper guiding pins 54 may be moved in the radial direction of the barrel when external force is applied to the straight-moving cylinder 52 in the optical axis direction, the taper guiding pins 54 and the parallel guiding pins 55 may be disengaged from the cam grooves if more than a certain amount of external force or external force is applied in another direction rather than the optical axis direction.